Structure-function studies are to be conducted with anthranilate synthase from Serratia marcescens. Group-specific reagents will be used to inactivate the enzyme and identify residues essential for NH3-dependent activity. Large amounts of E. coli amidophosphoribosyl transferase will be purified from a strain carrying a purF recombinant plasmid. The essential active site cystein will be labeled with 6-diazo-5-oxonorleucine, and an active site tryptic peptide will be isolated and sequenced. The nucleotide sequence of the purF gene will be determined, thus allowing the glutamine active site region to be placed in the sequence and a comparison with other glutamine amidotransferases to be made.